Cefn Cwm Coel (SN 891 647) – 500m
Sub-Uchaf deletion
There has been a deletion to a hill that is listed in the Yr Uchafion, with the summit height,
bwlch height and their locations, the drop and status of the hill confirmed by
a Trimble GeoXH 6000 survey conducted by Myrddyn Phillips on the 27th
February 2019, with the bwlch position based on LIDAR analysis conducted by
Aled Williams.
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| Cefn Cwm Coel (SN 891 647) |
The criteria for the list that this deletion applies to are:
Yr Uchafion – This is the draft title for the Welsh 500m P15s list that takes in all
hills in Wales at or above 500m in height with 15m minimum drop. Accompanying the main list are three sub
lists, these are; 500m Sub-Uchaf, 490m Sub-Uchaf and the Double Sub category, with
this hill being deleted from the 500m Sub-Uchaf category, the criteria for which
are all Welsh hills at or above 500m in height with 14m or more and below 15m
of drop. The list is co-authored by
Myrddyn Phillips and Aled Williams with the Introduction to the list being published on Mapping Mountains in November 2015.
The name of the hill is Cefn Cwm Coel and it is
adjoined to the Elenydd group of hills which is situated in central part of Mid
and West Wales (Region B, Sub-Region B2), and is positioned with the Claerwen
Reservoir to the west and the Garreg Ddu Reservoir to the east, and has the town
of Rhaesdr Gwy (Rhayader) towards its east north-east.
This hill was included when the original list of
Welsh 500m P15s was compiled and given an estimated drop of c 18m based on the
504m spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000
Explorer map and an estimated bwlch height of c 486m based on interpolation of
10m contouring between 480m – 490m.
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| Extract from the Ordnance Survey 1:25,000 Explorer map |
The details for this hill were reassessed when the
Ordnance Survey Vector Map Local hosted on the Geograph website became
available online, and which is entitled the Interactive Coverage Map. This mapping compliments the 504m summit spot
height given on the 1:50,000 and 1:25,000 map and also includes a 489m spot
height on the area of this hill’s bwlch, with these values giving this hill 15m
of drop, which is the minimum required for Uchaf status.
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| Extract from the Ordnance Survey Vector Map Local hosted on the Geograph website |
However, it was not until LIDAR became available
that the details for this hill could be accurately re-assessed. The LIDAR (Light Detection & Ranging)
technique produced highly accurate height data that is now freely available for
much of England and Wales.
LIDAR only covers the bwlch of this hill and
therefore its listed summit height remained at 504m, but as LIDAR analysis
produced a bwlch height of 489.6m positioned at SN 88436 65271 this hill was
reclassified from Uchaf status to 500m Sub-Uchaf status with 14m of drop.
The summit and bwlch of this hill have now been
surveyed with the Trimble GeoXH 6000 resulting in a 503.0m summit height and a
489.6m bwlch height, with these values giving this hill 13.4m of drop, which is
insufficient for its continued classification as a 500m Sub-Uchaf.
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| Gathering data at the summit of Cefn Cwm Coel |
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| Gathering data at the critical bwlch of Cefn Cwm Coel |
The full details for the hill are:
Group: Elenydd
Name: Cefn Cwm Coel
OS 1:50,000 map: 147
Summit Height: 503.0m (converted
to OSGM15)
Summit Grid Reference:
SN 89142 64733
Bwlch Height: 489.6m (converted
to OSGM15)
Bwlch Grid Reference:
SN 88436 65372
Drop: 13.4m
For the additions, deletions and reclassifications to Yr Uchafion / The Welsh 500m P15s
reported on Mapping Mountains please consult the following Change Registers:
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